The development of microelectromechanical systems (MEMS) has enabled the incorporation of a wide variety of sensors into mobile devices, such as cell phones, laptops, tablets, gaming devices and other portable, electronic devices. Non-limiting examples of sensors include motion or environmental sensors, such as an accelerometer, a gyroscope, a magnetometer, a pressure sensor, a microphone, a proximity sensor, an ambient light sensor, an infrared sensor, and the like. As the availability of sensors has increased, so too have the applications that utilize sensor data. For example, gesture recognition or orientation detection of a device equipped with sensors allows a user to input commands or data by moving the device or by positioning the device in a predetermined orientation. Any numbers of implementations exist, including allowing a user to select particular device functions by simply moving, shaking, or tapping the device. Such functionality can include motion gesture recognition implemented on motion sensing devices to allow a user to input commands or data by moving the device or otherwise cause the device to sense the user's motion. In light of this increased reliance on sensor information, the ability to provide relevant sensor data may be an important characteristic.
In many situations, operations known as sensor fusion may involve combining data obtained from multiple sensors to improve accuracy and usefulness of the sensor data, such as by refining orientation information or characterizing a bias that may be present in a given sensor. Although sensor fusion operations may provide enhanced data, the requirement of powering multiple sensor systems simultaneously may represent a significant expenditure of resources, both in terms of power consumption and computational demands. Particularly for mobile devices that may rely on a battery for energy or may have reduced computational abilities, the use of sensor fusion involving multiple sensor systems may represent an undesirably large portion of the resource budget. This is especially true for devices that have a small battery and where the specifications require a long battery life, so the user does not have the charge, or even replace, the battery very often. An example of such a device may be an portable activity monitoring device in the form of a bracelet or a (belt) clip. Accordingly, the techniques of this disclosure are directed to measuring linear acceleration using data from an accelerometer alone.